The disclosure relates generally to near-eye-display systems, and more specifically to waveguide displays that use holographic Bragg gratings.
Near-eye light field displays project images directly into a user's eye, encompassing both near-eye displays (NEDs) and electronic viewfinders. Conventional near-eye displays (NEDs) generally have a display element that generates image light that passes through one or more lenses before reaching the user's eyes. Additionally, NEDs in virtual reality systems and/or augmented reality systems have a design criteria to be compact and light weight, and to provide a two-dimensional expansion with a large eyebox and a wide field-of-view (FOV) for ease of use. In typical NEDs, the limit for the FOV is based on satisfying two physical conditions: (1) an occurrence of total internal reflection of image light coupled into a waveguide and (2) an existence of a first order diffraction caused by a diffraction grating element. Conventional methods used by the NEDs based on a diffraction grating rely on satisfying the above two physical conditions in order to achieve a large FOV (e.g. above 40 degrees) by using materials with a high refractive index, and thus, adds significantly heavy and expensive components to the NEDs. Specifically, in NEDs with waveguide display systems utilizing surface-relief grating elements, more than one waveguide is used for a full-color display because a single grating element with a single grating pitch cannot couple or decouple more than one channel without affecting the substantially large FOV of the NEDs. Accordingly, such NEDs scale up in thickness and weight with the number of channels and the number of planes for a multi-planar display. Furthermore, designing a conventional NED with two-dimensional expansion involving surface-relief grating elements not only diffract a light in-coupled into the waveguide but also diffract the light external to the NED towards the user's eyes, and generate undesirable ghost images.